Embodiments of the inventive concept relate to an oscillation circuit, and more specifically, to an oscillation circuit capable of rapidly and stably terminating an oscillation operation. Embodiments of the inventive concept also relate to semiconductor devices incorporating this type of oscillation circuit.
An oscillation circuit is one within a general class of circuits capable of generating a periodic signal having a constant pulse width. Oscillation circuits generate a periodic signal while so long as power is applied, and stop when power is cut off. Many different types of oscillation circuits are commonly used in semiconductor devices as (e.g.) clock generating circuits, voltage (control signal, or reference signal) generating circuits, etc.
Gated oscillation circuits are a particular subset of oscillation circuits and are capable of controlling an oscillation interval using a logic gate control signal (e.g., an oscillation enable signal). In general, a gated oscillation circuit includes a switch which is connected between specific nodes to control signal transmission. That is, when an oscillation enable signal is activated, the gated oscillation circuit turns ON the switch, such that a signal may be transmitted between nodes, thereby beginning the output of the periodic signal. When the oscillation enable signal is deactivated, the gated oscillation circuit turns OFF the switch to interrupt signal transmission between nodes and halts output of the periodic signal. That is, the oscillation circuit immediately turns OFF the switch when the oscillation enable signal is deactivated.
However, when the switch is turned OFF at the moment that the periodic signal being applied to a node is in an unstable state (i.e., during low-high or high-low transition), then some undefined intermediate level (not a logical “high” or “low” state) will be apparent at the node and a considerable amount of time may be required before the level of the periodic signal is returned to a stable high or low value at the node. Therefore, even if the switch is turned OFF, the oscillation circuit only stops the oscillation operation after some considerable period of additional time. Accordingly, various internal circuits routinely incorporated in contemporary semiconductor devices and operating in response to the periodic signal generated by an oscillation circuit may malfunction.